1. Field of the Invention
The present invention relates to a hydraulic brake pressure control system of the load responsive type for wheeled vehicles, and more particularly to a hydraulic brake pressure control system of the type which is arranged to control the rate of increase of the wheel cylinder pressure less than that of the master cylinder pressure depending upon the wheel load.
2. Description of the Prior Art
A conventional brake pressure control system as described above is well known which includes a hydraulic brake pressure control valve associated with a vehicle load sensing member. The control valve is provided therein with a spring loaded valve piston and is fixedly mounted on either wheel-axle or body frame parts separated from each other by a suspension system. The load sensing member is in the form of a leaf spring or a torque bar which is pivotally connected at its opposite ends to both the wheel-axle and body frame parts and in engagement with the outer end of the valve piston. The leaf spring or torque bar is flexed by relative displacement of the wheel-axle and body frame parts to control a biasing force acting on the valve piston in response to load on the wheels of the axle. In this type of load sensing member, shortening of the leaf spring or torque bar results in an increase of its spring constant. In a case where the mounting space for opposite ends of the leaf spring or torque bar is limited in a short distance, the biasing force on the valve piston excessively changes in response to relative displacement of the two masses separated by the suspension system because of high spring constant of the load sensing member. For this reason, such a load sensing member as a leaf spring or a torque bar may not be adapted to the hydraulic brake pressure control system.